Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/3612—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with organic compounds as principal constituents
  • B23K35/3616—Halogen compounds
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
  • B23K35/00—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting
  • B23K35/22—Rods, electrodes, materials, or media, for use in soldering, welding, or cutting characterised by the composition or nature of the material
  • B23K35/36—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest
  • B23K35/3612—Selection of non-metallic compositions, e.g. coatings, fluxes; Selection of soldering or welding materials, conjoint with selection of non-metallic compositions, both selections being of interest with organic compounds as principal constituents
  • B23K35/3618—Carboxylic acids or salts

Definitions

• This invention relates to a soldering flux and more particularly to a water-soluble soldering flux in which a residue of the flux remaining after soldering can be readily removed by washing with warm or cold water.
• a soldering flux is used in soldering to chemically remove oxide films from the metal surface to be soldered and from the molten solder surface, thereby exposing solderable metal surfaces. It is therefore indispensable in all soldering processes.
• a conventional flux used in soldering of electronic parts usually comprises rosin as the main activator.
• rosin as the main activator.
• Such a rosin-based flux has good solderability, is non-corrosive and non-toxic, and the flux residue remaining after soldering has good electrical insulation properties.
• rosin is thermoplastic in nature and it is non-reactive at room temperature but is activated at elevated temperatures.
• water-soluble soldering fluxes comprise as an activator an inorganic salt such as zinc chloride or ammonium chloride dissolved in glycerol or vaseline, or a hydrohalide salt of an amine dissolved in a water-miscible organic solvent.
• Another object of this invention is to provide a water-soluble soldering flux which does not appreciably decrease the insulation resistance of the soldered areas, if a slight amount of a residue of the flux is left after soldering.
• the present inventors have found that the use of a particular amine salt and a particular carboxylic acid in combination provides satisfactory results with respect to solderability, washability, and insulation resistance.
• the present invention provides a water-soluble soldering flux which comprises, as activators, tartaric acid and at least one ethanolamine salt selected from hydrohalide salts of mono-di-, and tri-ethanolamine. Less preferably, the ethanolamine salt may be replaced by the free base, i.e., mono-, di-, or tri-ethanolamine itself.
• the activators used in the water-soluble flux of the present invention are tartaric acid and at least one ethanolamine salt selected from a hydrohalide salt such as hydrochloride or hydrobromide salt of mono- di-, or tri-ethanolamine.
• Tartaric acid is a dihydroxy-dicarboxylic acid of the formula HOOC--CH(OH)--CH(OH)--COOH.
• L-tartaric acid is employed, but the D-isomer and a racemic body of tartaric acid may also be used in the present invention.
• ethanolamine salt useful as the other activator in the present invention is represented by the following general formula:
• X is a halogen and n is an integer from 1 to 3.
• the halogen includes fluorine, chlorine, bromine, and iodine.
• the halogen is chlorine or bromine, and more preferably it is chlorine.
• Any of mono-, di-, and tri-ethanolamine may be used in the form of its hydrohalide salt, which can be obtained by neutralizing the amine with a hydrohalogenic acid such as hydrochloric or hydrobromic acid.
• a hydrohalogenic acid such as hydrochloric or hydrobromic acid.
• a free ethanolamine i.e., mono-, di-, or tri-ethanolamine may be used in place of its hydrohalide salt, although it is less preferable.
• the use of a hydrohalide salt of an ethanolamine enhances the activity of the flux compared to the cases where the amine is used as a free base.
• the amounts of tartaric acid and the ethanolamine salt are such that the molar ratio of tartaric acid to ethanolamine salt is in the range of from 0.2:1 to 4:1 and more preferably from 0.4:1 to 2:1.
• the flux according to the invention when applied, for example, to a printed circuit board on which electronic parts are soldered, it can be used either in a liquid form or in a paste form.
• a liquid flux can be prepared by dissolving the above-mentioned two classes of activators in a solvent.
• Suitable solvents which can be used to prepare the liquid flux include water and water-miscible organic solvents
• Useful water-miscible solvents include lower alkanols such as ethyl alcohol and isopropyl alcohol; polyols such as glycerol, ethylene glycol, diethylene glycol, polyethylene glycol, and propylene glycol; ethers such a butyl carbitol; and the like.
• One or more of these solvents may be used in the flux.
• the solvent is a mixture of water and at least one water-miscible solvent and more preferably a mixture of water and at least one lower alkanol solvent such as isopropyl alcohol to which a small amount of glycerol or other viscous polyol solvent is added in order to increase the viscosity of the liquid flux, thereby facilitating coating with the flux.
• concentrations of the activators in the liquid flux are not critical and greatly depends on the particular solvent or solvents used.
• a paste flux can be prepared by admixing the activators with one or more water-miscible organic solvents which preferably contain at least one viscous solvent such as a polyol, e.g., diethylene glycol, glycerol, or polyethylene glycol.
• the solvents are used in a relatively small amount sufficient to form a paste.
• the flux of the present invention may further comprise a small amount of one or more additional activators which include urea, and organic acids other than tartaric acid, particularly monocarboxylic acids such as acetic acid, glycolic acid, and lactic acid.
• additional activators which include urea, and organic acids other than tartaric acid, particularly monocarboxylic acids such as acetic acid, glycolic acid, and lactic acid.
• the flux may further contain various additives unless they adversely affect the flux.
• the additives are a foaming agent, a thickening agent such as a polyol (which also serves as a water-miscible solvent), an antioxidant such as hydroquinone, and a surfactant, particularly a nonionic surfactant serving as a resin-scavenger.
• the water-soluble flux according to the present invention may be applied prior to soldering to those areas of a printed-circuit board, for example, to be soldered, by any suitable technique known in the art.
• a liquid flux can be applied to the board by bubble coating, dip coating, or spray coating, usually after electronic parts to be soldered are mounted on the board.
• a paste flux can be applied by printing or by using an automatic flux dispenser before electronic parts are mounted on the board.
• the flux may also be used to clean the surface of parts to be plated with a solder before the parts are plated, for example, by hot dipping.
• the flux may be admixed with a powder solder and one or more organic solvents to form a paste solder.
• Useful powder solders include powders of Sn-Pb, Sn-Pb-Ag, Sn-Ag, Sn-Pb-Bi, and Pb-In alloys.
• Water-soluble fluxes in liquid forms which contained one or two activators (Activator A alone, or Activators A and B) shown in Table 1 were prepared by dissolving the activator or activators in a solvent consisting of water, isopropyl alcohol, and glycerol.
• glycerol was present in an amount of 5% by weight based on the weight of the flux, and deionized water and isopropyl alcohol were used in equal weights.
• Activator A tartaric acid
• Activator B was used in an amount sufficient to obtain a predetermined molar ratio relative to Ingredient A (molar ratio of A:B) indicated in Table 1.
• Table 1 also includes the results of washability and insulation resistance tests of the fluxes, which were performed in the following manner.
• the flux to be tested was applied by dip coating to the predetermined areas on a printed circuit board on which electronic parts were to be mounted. The board was then dipped in a molten solder to deposit the solder on the predetermined areas. Subsequently, the soldered board was washed by successively dipping in three water baths at room temperature. The dipping period was one minute in each water bath, which was filled with running water to keep the water clean. After washing, the amount of ionic residues present on the printed circuit board was determined using an omega meter.
• the omega meter is a conductometric analyzer in which the ionic residues were dissolved and the electric conductivity of the resulting solution was measured. The amount of ionic residues determined was indicated in terms of micrograms ( ⁇ g) of NaCl per square inch of the board which produced the same magnitude of conductivity as the ionic residues did.
• a comb-shaped board for the measurement of insulation resistance (according to JIS Z 3197) was dip-coated with the flux to be tested and then subjected to soldering and washing in the same manner as in the washability test.
• the washed board was then kept for 96 hours in a thermo-hygrostated chamber at a temperature of 60° C. and a relative humidity of 90% and the insulation resistance of the board was measured in the chamber after 24 hours. It had been confirmed that the insulation resistance after 24 hours showed the same tendency as that after 96 hours.
• the soldering fluxes according to the present invention had excellent washability and insulation resistance in addition to good solderability. In other words, they showed smaller amounts of ionic residues remaining after washing and larger orders of magnitude of insulation resistance after storage in a humid environment. Thus, residues of the flux remaining after soldering can be readily removed by washing with water. Furthermore, even if some residues are left around the soldered areas after washing, they do not result in a significant decrease in insulation resistance which causes improper operation of the soldered parts. On the other hand, comparable fluxes of Runs Nos. 10 to 18 showed lower insulation resistance and most of them had inferior washability.

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Electric Connection Of Electric Components To Printed Circuits (AREA)

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Cited By (7)

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• 1989
  • 1989-11-24 JP JP1306059A patent/JPH03165999A/ja active Pending
• 1990
  • 1990-11-22 DE DE69028184T patent/DE69028184D1/de not_active Expired - Lifetime
  • 1990-11-22 EP EP90403301A patent/EP0430772B1/de not_active Expired - Lifetime
  • 1990-11-23 US US07/617,329 patent/US5074928A/en not_active Expired - Fee Related
  • 1990-11-23 AU AU66928/90A patent/AU635794B2/en not_active Ceased
  • 1990-11-23 KR KR1019900019064A patent/KR960001598B1/ko not_active IP Right Cessation
  • 1990-11-23 CA CA002030490A patent/CA2030490C/en not_active Expired - Fee Related

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